In the closing of binding combs using two bending rams, which combs are usually bent from wire, it is very difficult to achieve an accurately pre-determined profile of the closed binding comb, because the relative sliding relationships of the binding comb with respect to the bending rams are of essential importance. These sliding relationships depend not only upon the surface characteristics of the pressing surfaces of the bending rams, but also upon numerous other factors, for example also upon the material characteristics of the surface of the binding comb.
As a rule, a circular profile of the closed binding comb is the intended objective, wherein only the perforating prongs, formed by a C-profile arm, must enter the perforations of the block to be bound during the closing action with a corresponding change in position relative to the working ram associated with them, pass through this block and, finally, penetrate into gaps of the comb of the opposite C-profile arm. The reaction forces that hereby occur between the binding comb and one bending ram must be accepted for the greater part by the engagement between the other bending ram and the associated C-profile arm, it being possible for these reaction forces, acting in the circumferential direction of the binding comb as torsional forces, easily to result in a rotating displacement of the C-profile arm opposite to the perforating prongs relative to the associated bending ram. This displacement, however, leads to a squeezing of this C-profile arm towards the end of the closing bending operation and therefore to an out-of-true shape of the finished, closed binding comb which cannot be calculated. To enable the friction relationships between the binding comb and the two bending rams, which here play an important part, to be adjusted as favourably as possible, it has hitherto usually been attempted to make the sliding face of the working ram as smooth as possible by polishing and to provide the bending face of the opposite bending ram with the highest possible friction co-efficient (DE-PS No. 23 25 867).
It has also already been attempted (DE-PS No. 16 11 018 and DE-PS No. 24 03 154), to obtain an improvement in that the bending rams execute a curved movement differing from a linear movement, but this results in an extremely complicated mechanism of the apparatus, which furthermore is not very suitable for refitting to adapt to binding combs of different profiles.